Question

使用JPA和JSF的JavaEE应用程序具有一个Bill实体，该实体被分类为BilledBill，CancelledBill和RefundBill。我使用EclipseLink作为持久性提供程序。我想写一个查询，按类的类型对总数进行分组。我累了，但是失败了。有可能吗？

相关的构造函数如下。

public BillSummery(PaymentMethod paymentMethod, Class billClass, Double total, Double discount, Double netTotal, Double tax, Long count, BillType billType) {
    this.paymentMethod = paymentMethod;
    this.total = total;
    this.discount = discount;
    this.netTotal = netTotal;
    this.tax = tax;
    this.count = count;
    this.billType = billType;
    this.BillClass = billClass;
}

JPQL如下

String j = "select new com.divudi.data.BillSummery(b.paymentMethod, type(b), sum(b.total), sum(b.discount), sum(b.netTotal), sum(b.vat), count(b), b.billType) "
            + " from Bill b "
            + " where b.retired=false "
            + " and b.billTime between :fd and :td "
            + " group by b.paymentMethod, type(b), b.billType";

Answer 1

您使用哪种继承策略？

如果它包含一个鉴别符列，则可以始终将其映射为常规列，就像其他任何属性一样。然后它将可用于查询。

示例：

@Entity
@Inheritance(strategy = JOINED)
@DiscriminatorColumn(name = "dtype")
public abstract class Bill {

    @Column(name = "dtype", insertable=false, updatable=false)
    private String type;
    ...
}

话虽这么说，我会认真考虑扁平化继承结构。听起来好像Bill可以变成BilledBill或CancelledBill，所以Bill拥有status属性也许就足够了？

按JPQL中的对象类别分组

1 个答案: